docs: def _parseRuleset(self, src):
          """ruleset
          : selector [ ',' S* selector ]*
              '{' S* declaration [ ';' S* declaration ]* '}' S*
          ;
          """
          src, selectors = self._parseSelectorGroup(src)
          src, properties = self._parseDeclarationGroup(src.lstrip())
          result = self.cssBuilder.ruleset(selectors, properties)
          return src, result